1. Field of the Invention
The present invention concerns a suspension system for a turboshaft engine or similar at a pylon of an aircraft making it possible to ensure that said turboshaft engine is secured in total safety to the structure of the aircraft.
2. Description of the Related Art
The term suspension refers in a general manner to all the different parts necessary for securing the turboshaft engine to the pylon, such as notably the fastenings, articulations, axes, ball-and-socket joints, rods, arms, collars, fittings, etc. . . . that are usually found for this purpose.
In general, the suspension system is located and contained in specific planes of the turboshaft engine which are parallel to each other and at right angles with respect to the longitudinal axis of said turboshaft engine. In this way, it is made up by at least one front suspension plane located at an intermediate turboshaft engine casing and connecting same to the mounting beam in the pylon box, and by a rear suspension plane located at the exhaust casing of the turboshaft engine and connecting same to the beam of the pylon. Moreover, in addition to said two front and rear suspension planes, the suspension system as a whole includes thrust link means defined by rods when the turboshaft engine is attached under the wing of the aircraft as taught in document GB 1 236 917, or by an outer fan duct when the turboshaft engine is attached to the fuselage as claimed in the invention. The aim of the arrangement of the suspension system is notably to take up the forces exerted in the three directions or axes (roll, pitch, yaw) of an orthonormal frame of reference connected to the aircraft, as well as the momentums in said three axes.
Moreover, the invention concerns more particularly the safety of the suspension system made up notably by its front and rear planes. Therefore, in addition to the usual doubling of some of the parts listed above for the purposes of safety, the suspension system can include a so-called fail-safe supplementary suspension plane provided between the front and rear planes, in parallel with these latter. The aim of said intermediate suspension plane, in particular, is to take up the momentum of the forces around the yaw axis of the frame of reference (slippage momentum) in the event of a breakdown in the rear suspension system, notably when the turboshaft engine is located at the back of the fuselage of the aircraft, close to the wall thereof with the risk of said wall being perforated by fragments from the turboshaft engine and the suspension system. In this way, the turboshaft engine is held approximately in place in spite of said breakdown in the rear suspension system.
Said failsafe intermediate suspension system, disposed close to the rear suspension plane, includes a rod connecting the turboshaft engine to the beam of the pylon. The rod is mounted with sufficient clearance forming a free space so that no force passes through it while the rear suspension system remains operational and intact, such that the displacements and vibrations generated by the turboshaft engine during its operation and by the aircraft do not act on the rod. Said intermediate suspension plane is therefore on standby.
Although providing reinforced safety in the event of the rear suspension system breaking down, mounted in such a manner with clearance, in normal operation the connecting rod runs the risk of hitting the fastening with the turboshaft engine or the pylon due to the vibrations and other displacements produced and generated by the operation of same.
Moreover, at the time of installation, the engine being already supported by the suspension systems in a manner that is at least isostatic, the mounting of a classic standby supplementary rod calls for fine tolerances in the positioning thereof. Added to this is the restricted space between the turboshaft engine and the pylon which makes the mounting of the rod complicated.